Continuing advancements in electronic technology have led to the development of touch sensing technology for registering positional information and receiving user input. Within the broad category of touch sensing technology there exist capacitive sensing touch sensors, commonly referred to as capacitive touchpads or simply touchpads. In a touchpad, capacitance sensor elements are distributed underneath a sensing surface. When a user's finger (or some other type of object) is placed on the sensing surface, a capacitance is induced in the sensor elements.
Many of today's electronic devices now employ a touchpad as a user interface. Such devices include, but are not limited to, digital cameras, portable music players, personal digital assistants, portable laptop computers, cell phones, and touch screen display devices. For reasons of aesthetics and/or convenience of use, many of these types of devices utilize a round touchpad.
Conventional round touchpads commonly fall into two categories: round touchpads that measure angle only (e.g., jog dials, scroll dials, and the like); and round touchpads that measure a two-dimensional position using a truncated rectangular grid of sensor elements. Round touchpads that measure angle provide only one axis of positioning information—that is, they can measure an angle in the circumferential direction, but they cannot discern distance in the radial direction.
Round touchpads that use a truncated rectangular sensor grid can be problematic because some of the sensor elements are shorter in length than others. A background capacitance measured on a longer sensor element may be different from a background capacitance measured on a shorter sensor element. Furthermore, longer and shorter sensor elements may respond differently to the same object. Some type of compensating effect may be applied to the sensor output signals in order to offset the effect of unequal sensor element length.
Accordingly, a touchpad that can be used to accurately indicate the position of an object or finger, but that avoids the problems mentioned above, would be advantageous.